MUSEUM OF COMPARATIVE ZOOLOGY. 



167 



Genus PENTACRINUS Miller. 



( Usually 15-18 internodal joints. The i 

 I hypozygal does not share in the cirrus- 



,-,■_. , I sockets. Usually more than three joints I „,,.,„■„ t;„„ 



1 tout f I ^'^''''"' "^^ irregular am. divisions, f '«'«"* ^''^°- 

 T 4S*iiiiit3 " -! ^'""'I'^Jo'"'''* li^'^e forward-projecting I 



The two 

 outer radials 

 and the lirst 

 two joints he- 

 yond each 

 axillary unit- 

 ed by syzy- 

 gies. 



The two 

 outer radials 

 and the first 

 two joints 

 beyond thera 

 united by lig- 

 amentous ar- 

 ticulatious. 



Five cir- 

 ri at each 

 uode. 



Rays may di- 

 vide five times. 



processes. 

 6-8 internodal joints. 



The hypozy 



gal shares in the cirrus-sockets. Ouly 

 two or three joints between the regu 

 '- lar arm divisions. 



'.I 



mulUri 



Oerst. 



15-25 cirrus- 

 joints. Rays 

 ouly divide 

 three times ; 

 each division " 

 of two joints 

 united by syz- 



ygy- 



One or two internodal joints 



macharanus 

 Wy. Th. 



35-45 internodal joints iwymllctkom. 



' \ S07U Jeiir. 



Two and three cirri alternately at successive nodes. Rays divide 1 ,, 



three times ; each division of two jomts united by sjzygy. lour in- J 



ternodal joints. ) ' *'P' 



Ten arms. The third brachial a syzygy, with angular syzygial faces. I nnresianus 

 First pinnule on the second brachial. 8-17 internodal joints. ( \Vy. Th. MS. 



Rays may divide three 

 times. Tlie .second free bra- 

 chial a syzygy. Pinnule on 

 first brachial. 



5-7 internodal joints. Nodal joints 1 

 not enlarged, and the hypozvgal shar- I l. i, ■ 

 ing but litde in the cirrus-sockets. Sy- f"'"*^' ^• 

 zygial faces angular. J 



pp. 



11 or 12 internodal joints. Nodal 

 joints enlarged and i>rnjecting, and the \decorus 

 hypozygal grooved to receive the cirrus- f Wy. Th. 



bases. Syzygial faces nearly plane. J 



It will be seen from the preceding table that the Caribbean species of 

 Pentacrinus are equally divided between the two groups into which the 

 eight recent species of the genus very naturally fall. Of the remaining 

 types, P. wyvUle-thomsoni and P. madearanus both occur in the Atlantic, 

 the former off the Portuguese coast and the latter off Pernambuco. 

 P. alternicirra and P. naresianus were dredged by the " Challenger " oft 

 the Kermadec Islands, and also to the southeast of the Philippines, the 

 latter species also occurring at another station in the South Pacific, 



Most of the Pentacrinidce obtained by the " Challenger " in the Pacific 

 represent a new and very curious-^type, which Sir Wyville Thomson des- 

 ignated by the name of Metacrinus in a memorandum on one of his 

 plates. It is readily distinguished from Pentacrinus by having, not three, 

 but from four to six radials. The second of these is a syzygial joint, and 

 bears a pinnule, as do all the following joints below the radial axillary. 

 There are numerous otlier minor differences between Metacrinus and Pen- 

 tacrinus which need not be considered here. 



The examination of this large series of Pentacrinida; fully confirms 

 the views which I have expressed elsewhere * as to the difficulty of rc- 



* Jouni. Linn. Soc, VoL XV. p. 210. 



